Concrete pole and method of reinforcing same

Abstract: A concrete pole (9) having an improved elasticity by reinforcement of a simple construction is provided. A reinforcing layer (11) of a fibre-reinforced composite material is provided on part of the outer circumference of the concrete pole (9) comprising reinforced concrete. The reinforcing layer (11) covers a depth of at least 30 cm and a height of at least 100 cm relative to the ground level upon burying of the concrete pole (9). Reinforcing fibres (4) of the reinforcing layer (11) are oriented in the axial direction of the reinforced concrete. The total cross-sectional area (S R ) and modulus of elasticity (E R ) of the reinforcing fibres (4) of the reinforcing layer (11) satisfy the following relational formula relative to the total cross-sectional area (S S ) and modulus of elasticity (E S ) of the axial reinforcing bar of the reinforced concrete: 0.06 < (E R .S R )/(E S .S S ) < 3.0

Description: The present invention relates to a concrete pole such as an electricity pole, of the kind generally known as for example in US-A-5 043 003 or EP-A-0 173 446. Concrete poles are widely used for many electric poles including those for power distribution in urban areas, and those for power supply for electric trains. In general, a concrete pole is formed into a hollow elongate structure made of reinforced concrete by using a cage of reinforcing bars formed into a desired shape and placing concrete by centrifugal casting in and outside this cage. The pole may be cylindrical, for example a right circular cylinder, or tapered. When an automobile collides with a concrete pole on the road, the concrete pole first deflects and then resumes its original vertical posture by elasticity. When the impact is strong and results in a large deflection, however, the reinforcing bars in the interior are plastically deformed with an elongation of only 0.2% and the concrete pole cannot resume the original posture, but remains deformed. A concrete pole thus deformed is a traffic hindrance and can be dangerous. Under such circumstances as described above, there is a demand for a concrete pole having an improved elasticity, which, even after occurrence of such a large deflection as to cause plastic deformation of reinforcing bars therein, can resume the original vertical posture thereof by elasticity, and does not form a traffic hindrance or a danger for cars and electric trains. A concrete pole provided with such properties has not as yet been proposed. The present invention aims to provide a concrete pole having an improved elasticity. According to a first aspect of the present invention there is provided a concrete pole which comprises reinforced concrete of elongate shape having reinforcing bars characterised in that part of the outer circumference of said concrete pole is reinforced by a reinforcing layer of a fibre-reinforced composite material which is composed of reinforcing fibres and a thermosetting resin impregnated in the reinforcing fibres; said reinforcing layer covers a depth of at least 30 cm and a height of at least 100 cm relative to the ground level upon burying of said concrete pole; the reinforcing fibres of said reinforcing layer are oriented in the axial direction of said reinforced concrete; and the total cross-sectional area (S R ) and modulus of elasticity (E R ) of the reinforcing fibres of said reinforcing layer satisfy the following relational formula relative to the total cross-sectional area (S S ) and modulus of elasticity (E S ) of the reinforcing bars in the axial direction of said reinforced concrete: 0.06 < (E R .S R )/(E S .S S ) < 3.0 According to a second aspect of the present invention, there is provided a method of reinforcing a concrete pole by providing a reinforcing layer of a fibre-reinforced composite resin material, which is composed of reinforcing fibres and a thermosetting resin impregnated in the reinforcing fibres, on part of the outer circumference of a concrete pole comprising reinforced concrete of aN elongate shape having reinforcing bars, wherein said reinforcing layer covers a depth of at least 30 cm and a height of at least 100 cm relative to the ground level upon burying of said concrete pole; the reinforcing fibres of said reinforcing layer are oriented in the axial direction of said reinforced concrete; and the total cross-sectional area (S S ) and modulus of elasticity (E S ) of the reinforcing bar in the axial direction of said reinforced concrete: 0.06 < (E R ·S R )/(E S ·S S ) < 3.0 Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which: Fig. 1 is a cross-sectional view illustrating an embodiment of the concrete pole of the present invention; Fig. 2 is a front view illustrating the same embodiment as above; Fig. 3 is a perspective view illustrating a partially enlarged reinforcing layer provided on the concrete pole in the same embodiment; Fig. 4 is a plan view illustrating the test for investigating the reinforcing effect of a concrete pole of the present invention; Fig. 5 is a sectional view illustrating a unidirectional reinforcing fibre sheet useful for reinforcing the concrete pole of the present invention; Fig. 6 is a sectional view illustrating a method of the present invention; Fig.7 is a sectional view illustrating another method of the present invention; and Fig. 8 is a sectional view illustrating a further method of the present invention. Fig. 1 is a cross-sectional view illustrating an embodiment of the concrete pole of the present invention; Fig. 2 is a front view of the concrete pole of the present invention; and Fig. 3 is a perspective view illustrating a partially enlarged reinforcing layer provided on the concrete pole shown in Figs. 1 and 2. As shown in Figs. 1 and 2, a concrete pole 9 is formed as a hollow cylinder made of reinforced concrete formed by placing concrete in and outside a cage of reinforcing bars 10 formed in a substantially cylindrical shape, by centrifugal casting. The concrete pole 9 is installed vertically on the ground level with a lower portion thereof buried into the ground 12. When installing the concrete pole 9, concrete 13 is placed around the buried portion 9a buried in the ground 12 of the concrete pole 9. In this embodiment, the concrete pole 9 represents an electric pole having a straight cylindrical shape, which has, for example, a length of 10m, an outside diameter of 35 cm and a buried portion 9a of 170 cm. According to the present invention, the concrete pole 9 is provided, around upper and lower portions with the ground level of the ground 12 in between, with a reinforcing layer 11 made of a fibre-reinforced composite resin material in which reinforcing fibres 4 are oriented in the axial direction of the concrete pole 9. The present inventors carried out extensive studies to develop a high-elasticity concrete pole. The findings obtained as a result teach that, while a concrete pole 9 comprising reinforced concrete alone loses elasticity with an elongation of about 0.15%, carbon fibre, for example, shows such a high elasticity as to serve as an elastic body with an elongation of up to about 1.5%. Improved elasticity of the concrete pole 9 is obtained by reinforcing it with a fibre-reinforced composite material using the carbon fibre. Even when deflection sufficient to cause plastic deformation of the reinforcing bars 10 in the interior occurs, the concrete pole 9 resumes the original vertical posture thereof by elasticity. In the present invention, a reinforcing layer 11 made of a fibre-reinforced composite material using high-elasticity reinforcing fibres 4 such as carbon fibre is provided around portions above and below the ground level of the concrete pole 9, with the orientation of the reinforcing fibres aligned with the axial direction of the concrete pole 9. For the purpose of providing the concrete pole 9 with the reinforcing layer 11 of the fibre-reinforced composite material as described above, it suffices to use a unidirectional reinforcing fibre sheet as described below. Fig. 5 is a sectional view illustrating a typical unidirectional reinforcing fibre sheet 1 used for the application of the reinforcing layer 11 of the fibre-reinforced composite material in the present invention. This unidirectional reinforcing sheet 1 is formed by providing an adhesive layer 3 on a substrate sheet 2, and arranging reinforcing fibres 4 in one direction through the adhesive layer 3 on the sheet 2. Details of the reinforcing fibre sheet 1 will be described later. As shown in Fig. 3, the reinforcing layer 11 of the fibre-reinforced composite material can be provided on the concrete pole 9 by winding the reinforcing fibre sheet 1 around the surface of prescribed portions of the concrete pole 9 while causing the orientation of the reinforcing fibres 4 of the reinforcing fibre sheet 1 to agree with the axial direction of the concrete pole 9, curing a thermosetting resin impregnated into the reinforcing fibres 4 before or after winding, and thus converting the reinforcing fibre sheet 1 into a fibre-reinforced composite material. According to the results of an experiment carried out by the present inventors, it is necessary that the total cross-sectional area (S R ) and modulus of elasticity (E R ) of the reinforcing fibre should satisfy the following relational formula relative to the total cross-sectional area (S S ) and modulus of elasticity (E S ) of the reinforcing bar 10 in the axial direction of the concrete pole 9: 0.06 < (E R .S R )/(E S .S S ) < 3.0 in order to provide the concrete pole 9 with elasticity up to a large elongation exceeding the elongation causing plastic deformation of the reinforcing bar 10 through reinforcement by means of the reinforcing layer 11 made of the fibre-reinforced composite material. A relation (E R .S R )/(E S .S S ) ≤ 0.06 leads only to a slight restoration force of the concrete pole 9, so that the concrete pole 9 can not resume the original shape, having residual permanent deflection. A relation 3.0 ≤ (E R .S R )/(E S .S S ) results, on the other hand, in an excessively high stiffness so that application of a large deflection causes the concrete pole 9 fractures on the compression side. The coverage of reinforcement by the reinforcing layer 11 of the fibre-reinforced composite material should include, for ensuring an elasticity upon collision of a car, for example, a depth of at least 30 cm and a height of at least 100 cm from the ground level of the concrete pole 9. The reinforcing layer 11, instead, may be provided over the entire length, considering the location of service of the concrete pole 9. The reinforcing layer 11 of the fibre-reinforced composite material may be provided before or after installation of the concrete pole 9. For the purpose of protecting the reinforcing layer 11 and preventing peel off thereof, a second reinforcing layer similar to the reinforcing layer 11 and made of a similar fibre-reinforced composite material may be provided thereon such that the orientation of the reinforcing fibres of the second reinforcing layer coincides with the circumferential direction of the concrete pole 9. In the present invention, as described above, the unidirectional reinforcing fibre sheet 1 formed by arranging reinforcing fibres 4 in one direction through an adhesive layer 3 on a substrate sheet 2 is used for providing the reinforcing layer 11 of the fibre-reinforced composite material on the concrete pole 9. As for the substrate sheet 2 of this reinforcing fibre sheet 1, there may be used scrim cloth, glass cloth, mould release paper, nylon film and the like. When scrim cloth or glass cloth is used for the substrate sheet 2, the thermosetting resin can be impregnated from the side of the sheet 2 into the reinforcing fibres 4. To keep a level of flexibility and to permit support of the reinforcing fibres 4, the substrate sheet 2 should have a thickness within a range of from 1 to 500µm, or more preferably, from 5 to 100µm. Any adhesive which can at least temporarily stick the reinforcing fibres 4 onto the substrate sheet 2 may in principle be used for forming the adhesive layer 3. It is preferable to use a resin having a satisfactory affinity with a thermosetting resin; when an epoxy resin is used as the thermosetting resin, for example, it is recommended to use an epoxy type adhesive. Because the adhesive has to bond the reinforcing fibres 4 only temporarily, the thickness of the adhesive layer 3 should be within the range 1 to 500µm or, more preferably, 10 to 30µm. The reinforcing fibres 4 arranged in one direction of the reinforcing fibre sheet 1 are provided on the substrate 2 by unidirectionally arranging fibre bundles each binding a plurality of filaments or bundles gathering slightly twisted filaments through the adhesive layer 3 onto the substrate sheet 2 and pressing them from above. Pressing of the fibre bundles slightly scatters the fibre bundles and the filaments thereof are stuck in one direction through the adhesive layer 3 onto the substrate sheet 2 in a state in which the filaments are laminated into a plurality of laminations through connection by a bundling agent or twisting, thus giving the desired reinforcing fibre sheet 1. At this point of the process, fibre bundles may be densely arranged close to each other or may be sparsely arranged at intervals. The filaments of a fibre bundle may or may not be opened. The degree of pressing depends upon the target thickness of the arranged reinforcing fibres 4. As an example, carbon fibre bundles each containing about 12,000 filaments of a diameter 5 to 15µm should be pressed to cause the filaments to form a width of about 5mm. Applicable thermosetting resins for impregnation of the reinforcing fibres 4 include epoxy, unsaturated polyester, vinyl ester and urethane thermosetting resins. Particularly, a room-temperature setting type resin made to set at the room temperature by adjusting the curing agent and/or the curing accelerator for the thermosetting resin is suitably applicable. When using an ordinary thermosetting resin, it is necessary to cure the thermosetting resin impregnated into the reinforcing fibres through heating of the reinforcing fibre sheet wound on the concrete pole. It is, however, possible when using a room-temperature setting resin, to cause curing of the thermosetting resin by leaving the reinforcing fibre sheet wound on the concrete pole after impregnation of reinforcing fibres with the resin. When providing a reinforcing layer of a fibre-reinforced composite material on an already installed concrete pole, therefore, operations may be carried out at a high efficiency. Impregnation of the reinforcing fibres 4 with a thermosetting resin may be conducted before or after winding the reinforcing fibre sheet 1 onto the concrete pole. When the thermosetting resin is impregnated after winding, a resin-permeable sheet such as scrim cloth or glass cloth may be used as the substrate sheet 2 of the reinforcing fibre sheet 1, as described above. According to one embodiment, application of the reinforcing layer 11 of the fibre-reinforced composite material using the reinforcing fibre sheet 1 is effected as follows. As shown in Fig. 6, this operation comprises the steps of applying a thermosetting resin 5 onto the surface of a desired portion centring around the ground level of the concrete pole 9 into a thickness of, for example, about 100µm, then winding one or more reinforcing fibre sheets 1 by aligning the direction of the reinforcing fibres 4 with the axial direction of the pole 9, and impregnating the reinforcing fibres 4 with the thermosetting resin 5 by pressing. When winding the second sheet 1 onto the already wound sheet 1, the thermosetting resin may be applied again onto the substrate sheet 2 of the first sheet 1. Then, after impregnating operation of the thermosetting resin by means of a hand roller, for example, the layer is covered by winding a keep tape. Subsequently, the thermosetting resin impregnated into the reinforcing fibres 4 is cured by heating the reinforcing fibre sheet 1, or when using a room-temperature setting resin, by leaving the reinforcing fibre sheet 1 as it is, thus converting the reinforcing fibre sheet 1 into a fibre-reinforced composite material. The reinforcing layer 11 comprising the fibre-reinforced composite material is thus applied onto the concrete pole 9. An alternative practice comprises the steps of applying, for impregnation, the thermosetting resin onto the reinforcing fibres 4 on the reinforcing fibre sheet 1 with the use of an appropriate application means such as a roller, a brush or spraying, and then as shown in Fig. 7, winding one or more reinforcing fibre sheets onto the surface of a desired portion centring around the ground level of the concrete pole 9 with the reinforcing fibres 4 on the pole 9 side while considering the direction of the reinforcing fibres 4. The subsequent operation is only to provide a covering coat, and curing the thermosetting resin to convert the sheet 1 into a fibre-reinforced composite material. A further alternative practice comprises the steps of using a reinforcing fibre sheet 1 having a resin-permeable substrate sheet 1, applying, as the primer 6, a resin of the same type as the thermosetting resin onto the surface of a desired portion of the concrete pole 9, as shown in Fig. 8, winding one or more reinforcing fibre sheets 1 thereonto while considering the orientation of the reinforcing fibres 4, and then causing impregnation of the thermosetting resin 5 onto the substrate sheet 2 of the outermost sheet 1 by means of a roller, for example. The subsequent steps are the same as above: providing a cover coat, and hardening the thermosetting resin to convert the sheet 1 into a fibre-reinforced composite material. In all of the above-mentioned embodiments, the reinforcing fibre sheet 1 has been wound with the reinforcing fibres 4 directed toward the concrete pole 9. It is however possible also to form a reinforcing layer 11 of a fibre-reinforced composite resin material by winding the reinforcing fibre sheet 1 with the substrate sheet 2 directed toward the pole 9. The above embodiments have covered the case of an electric pole. However, the present invention is not limited to such a case, but is also applicable mutatis mutandis to a bridge pier, a post for an indication panel or a post for a signboard, for example. Some examples of the present invention are now described below. Examples 1 to 5 and Comparative Examples 1 to 5: A reinforcing layer 11 of a fibre-reinforced composite material was formed to reinforce a concrete pole 9 by using a unidirectional reinforcing fibre sheet of any of various reinforcing fibres, and a bending test was carried out in accordance with JIS-A5309. The tested concrete pole was a straight cylindrical reinforced concrete pole of 10-35-N5000, i.e. having a length of 10m, an outside diameter of 35 cm and a design bending moment (M) of 5,000 kgm. As shown in Fig. 4, a portion of the concrete pole 9 from the base end thereof to a position of 1.7m (corresponding to the buried depth) was fixed, and a load P was applied by hooking a wire at a position of 8,050mm from the fixed end to carry out a cantilever bending test. After causing deflection until a displacement of 400mm was reached at a position of 7m from the fixed end, the load was eliminated to measure residual deflection at a position of 7m, and a residual deflection of up to 100mm was determined to represent a good result. A reinforcing layer 11 of a fibre-reinforced composite material was formed by applying a reinforcing fibre sheet, impregnated with a thermosetting resin, around a prescribed portion with the fixed end upon the test 1.7m from the base end; corresponding to the ground level) in between so that the reinforcing fibres were arranged in the longitudinal direction of the concrete pole 9, and curing the resin. The effects of the kind of the reinforcing fibre, the amount of application (cross section), the range of reinforcement and the residual deflection were determined. Modulus of elasticity of reinforcing fibre: E R in kgf/cm 2 , Total cross-sectional area of reinforcing fibre: S R in cm 2 , Modulus of elasticity of reinforcing bars used: E S in kgf/cm 2 (up to 2,000,000 kgf/cm 2 ), Total cross-section area of reinforcing bars used: S S , in cm 2 (up to 6.4 cm 2 ). The results were arranged in terms of the ratio (E R .S R )/(E S .S S ) on the assumption as described above. Reinforcement covered a portion lower than the fixed end (depth) of L G , and a portion higher than the fixed point (height) of L A . Details of the Example 1 were as follows. A portion of a depth of 1m and a height of 5m from the fixed end position of the concrete pole was reinforced by the use of a unidirectional reinforcing fibre sheet of carbon fibre (carbon fibre sheet). A "FORCA TOW SHEET FTS-C1-17" manufactured by Tonen Co. Ltd. was used as the carbon fibre sheet, the "FR RESIN FR-E3P", an epoxy resin adhesive, manufactured by Tonen was used as the impregnating resin. The procedure for application comprised the steps of preparing a mixture of the above-mentioned thermosetting resin and a curing agent mixed at a prescribed ratio, applying the resin mixture in an amount of about 0.500 kg/m 2 to the portion of the concrete pole to be reinforced, then applying and impregnating the carbon fibre sheet with the said resin mixture so that the fibre orientation was in alignment with the axial direction of the concrete pole, and making the sheet into a composite material by curing. One unidirectional carbon fibre sheet was applied. After application, the reinforced concrete pole was maintained at a temperature of up to 20°C for a week for curing, and then the above-mentioned bending test was carried out to measure residual deflection of the concrete pole. E R = 2,350,000 kgf/cm 2 , S R = 1.06 cm 2 , E S = 2,000,000 kgf/cm 2 , S S = 1.06 cm 2 . This resulted in (E R .S R )/(E S .S S ) = 0.19, L G = 100cm and L A = 500cm. The examples 2 to 5 and the Comparative Examples 1 to 5 were also carried out as in the Example 1. In each of the Examples 1 to 4, as shown in Table 1, a unidirectional reinforcing fibre sheet of carbon fibre was used, and in the Example 5, a unidirectional fibre sheet of glass fibre was used, to form the reinforcing layer of the fibre-reinforced composite material provided on the desired portion of the concrete pole at the ground level for reinforcement. There was only slight residual deflection in the concrete pole after the bending test,thus a good result was obtained in terms of improvement of elasticity by reinforcement. In contrast, in the Comparative Example 1, in which no reinforcement was applied, as well as in the Comparative Example 2, in which the lower range of reinforcement L G was small, and in the Comparative Example 3, in which a glass fibre plain-woven cloth was used and the ratio (E R .S R )/(E S .S S ) was lower than the range in the present invention, the concrete pole had a large residual deflection after the bending test, and a satisfactory result in improving elasticity was unavailable. In the Comparative Example 4, in which, while using a unidirectional carbon fibre sheet, the ratio (E R .S R )/(E S .S S ) was over the range in the present invention, the concrete pole suffered from compression fracture with an initial deflection of 350mm in the bending test. In the Comparative Example 5, in which, while using a unidirectional carbon fibre sheet, the upper range of reinforcement L A was small, the reinforcing layer peeled off with an initial deflection of 380mm.

Claims: A concrete pole (9) which comprises reinforced concrete of an elongate shape having reinforcing bars (10) whereby part of the outer circumference of said concrete pole (9) is reinforced by a reinforcing layer (11) of a fibre-reinforced composite material (1) which is composed of reinforcing fibres (4) and a thermosetting resin impregnated in the reinforcing fibres (4); said reinforcing layer (11) covers a depth of at least 30 cm and a height of at least 100 cm relative to the ground level upon burying of said concrete pole (9); the reinforcing fibres (4) of said reinforcing layer (11) are oriented in the axial direction of said reinforced concrete; and the total cross-sectional area (S R ) and modulus of elasticity (E R ) of the reinforcing fibres (4) of said reinforcing layer (11) satisfy the following relational formula relative to the total cross-sectional area (S S ) and modulus of elasticity (E S ) of the reinforcing bars (1) in the axial direction of said reinforced concrete: 0.06 < (E R .S R )/(E S .S S ) < 3.0 A concrete pole (9) as claimed in claim 1, wherein the reinforcing fibre (4) of said reinforcing layer (11) is a fibre selected from the group consisting of carbon fibre and glass fibre. A concrete pole as claimed in claim 1 or 2, wherein the resin of said reinforcing layer (11) is a resin selected from the group consisting of epoxy, unsaturated polyester, vinyl ester or urethane resins. A concrete pole (9) as claimed in claim 1, 2 or 3, wherein said concrete pole is an electric pole, a bridge pier, a post for an indication panel, or a post for a signboard. A method of reinforcing a concrete pole (9) by providing a reinforcing layer (11) of a fibre-reinforced composite material, which is composed of reinforcing fibres (4), and a thermosetting resin impregnated in the reinforcing fibres (4) on part of the outer circumference of a concrete pole (9) comprising reinforced concrete of elongate shape having reinforcing bars (10), wherein said reinforcing layer (11) covers a depth of at least 30 cm and a height of at least 100 cm relative to the ground level upon burying of said concrete pole (9); the reinforcing fibres (4) of said reinforcing layer (11) are oriented in the axial direction of said reinforced concrete; and the total cross-sectional area (S R ) and modulus of elasticity (E R ) of the reinforcing fibres (4) of said reinforcing layer (11) satisfy the following relational formula relative to the total cross-sectional area (S S ) and modulus of elasticity (E S ) of the reinforcing bars (10) in the axial direction of said reinforced concrete: 0.06 < (E R .S R )/(E S .S S ) < 3.0 A method of reinforcing a concrete pole (9) as claimed in claim 5, wherein said reinforcing layer (11) is formed by impregnating with a thermosetting resin a reinforcing fibre sheet which is formed by arranging reinforcing fibres (4) in one direction through an adhesive layer (3) to a substrate (2), applying the reinforcing fibre sheet (1) onto the outer circumference of the concrete pole (9) and then curing the resin. A method of reinforcing a concrete pole as claimed in claim 5, wherein said reinforcing layer (11) is formed by applying a reinforcing sheet, which is formed by arranging reinforcing fibres in one direction through an adhesive layer (3) to a substrate (2), onto part of the outer circumference of said concrete pole (9), impregnating the reinforcing fibre sheet (1) with a thermosetting resin, and then curing the resin. A method of reinforcing a concrete pole as claimed in claim 5, wherein said reinforcing layer (11) is formed by coating a thermosetting resin (5) onto part of the outer circumference of said concrete pole (9), applying a reinforcing sheet (1), which is formed by arranging reinforcing fibres (4) in one direction through an adhesive layer (3) to a substrate (2), onto the resin coated circumference of the concrete pole (9), pressing and impregnating the reinforcing fibre sheet (1) with the thermosetting resin, and then curing the resin. A method of reinforcing a concrete pole as claimed in any one of claims 5, 6, 7 or 8, wherein the reinforcing fibres (4) of said reinforcing layer (11) are selected from the group consisting of carbon fibre and glass fibre. A method of reinforcing a concrete pole as claimed in any one of claims 5, 6, 7, 8 or 9, wherein the resin of said reinforcing layer (11) is selected from the group consisting of epoxy, unsaturated polyester, vinyl ester and urethane resins.

Inventors: SAITO MAKOTO, TANAKA YOSHINORI, SAITO, MAKOTO, TANAKA, YOSHINORI, SAITO, MAKOTO, C/O TONEN CORP., CORPORATE RES., TANAKA, YOSHINORI, C/O TONEN CORP., CORPORATE RES.
Applicants: TONEN CORP, TONEN CORPORATION
Application year: 1994
Main classification: E04H12
IPC codes: E04H12, E04G23